Fix pagination for all DRF APIs by inheriting from MarketplaceView (bug 945709)

https://bugzilla.mozilla.org/show_bug.cgi?id=945709

Our custom pagination serializer, added in bug 910571 to support tastypie-like offset-based pagination, can't work alone. The views need to handle the pagination correctly themselves (they need to accept the 'offset' parameter). So, I moved the paginate_queryset() method to `MarketplaceView` and made every view inherit from it.